How does one go about removing weakening, and corrosion and the likes? I know there are potions, but I can only start with one potion, and unless I one-shot the enemies, i often get two stacks of said debuff per fight. They don't dissipate upon level, so what do I do?

You can either buy another one of those potions (i.e. burn salve fortitude tonic) or you can use GG's cleansing boon. Other than that they are unremovable, so I suggest you just try to avoid them completely.

I always just save those enemies till I am a higher level and then one shot them without incurring weakening or corrosion as they are very bad. (weakening especially)

We made an expansion and it is awesome. Really, you should check it out, especially if you're looking for some extra challenge.

Yeah, you're better off just not fighting these kinds of enemies to avoid those penalties. Weakening in particular can completely cripple your character. Corrosion isn't quite as bad, since its effect doesn't accumulate as you gain levels. Attack bonus, however, hurts most at higher levels so you'll end up paying big time for even a small amount of weakening.

High damage characters or magic where possible. CYDSTEPP Rogue works well as always. Even without it, if you get a large mana pool use fireballs to soften your target and finishing with a regular attack isn't too bad. May not be that effective on the higher level meat men though.

You gotta start fighting the bosses after the meat men become corrosive. You have to be very frugal with your kills to get the most out of the meat men before they become corrosive. Yes, that means you probably have to start the boss battle around level 6.